Direction finder



May 6, 1947. w. CARLSON 2,419,987

DIRECTION FINDER Filed July so, 1942 man/van fill OFF COURSE 7'0 HIGH? .11 a x I 1.9 1 7 F/lD/O 17565 I VB)? Zmventor DEC/LEM?) Gttomeg Patented May 6, 1947 Wendell Carlson;v

Haddonfield Nr J ass ignorto" Radio- Corporation of- America a:- corporatiom ofDclaware- Application-July so, 1942;,- seriar teasin- Claims. (crest-ii 1': This invlention relateef tm' radio direction finders; andi more particularly to direct:v indicating systems of the type? in which: the output: of a directional antenna combined. with that of a nori directionalvantenna toiprovide a left right indication of the: deviation ofthe directional an tenna from-theazimuth oi arrival of asignal.

\ Systems of thistwpe usuallyoomprise adirective antennat-anon -directive antenna, and a common receiver for: both antennas; with some s'ort of switchingnieans arranged to reverse periodically the polarity of one of theantennas. The-figureof-eight directive 1 patterns of the directive antienna; which may be a? loop, are thus combined with -the circular pattern of the non-directional afintennwso as to produce alternatelyoverlapping caidioid patterns; A center-zero indicator is connected in the receiver output and reversed synchronously with theantenna switching; when theaxis the loep is-directed toward the transmitting station,- the signals received on the two cardioids are-equal; and the-indicator is=not defleotedi Wlien-the signal-arrivesin-some dire'ctioma-t an angle: other than along the loop axis? thesignal picked up" fromthe field correspending toone'cardicid patterri is greater than that" picked up fromtliefield corresponding to the other cardioid pattern, and the indicator is accordingly deflected to the -left' or right; as the easemay be: The periodic antenna reversal-maybe accordplishedby balanced modulators; using vacuum tubes; or by vibratory or rotary switches? Each of these methods-"has its-advantages: as well as tlie disadvantages of'a'sbmewhat complicated organization': In"a"mobil"installation, on'aircr'aft; for example; simplicity'and lightnessarematters of'primary importance. I

Accordingly; it object of this invention to provide improved method of and meansfor combining, the outputs of the antennas in an automaticleft-rightdirection indicator;

Another object to provide an improved method of" and n'ieans for modulating the loop signal without-resorting, tmvacuum tube modulators or movifigp'artsl 1: HA further: object" is's to provide: improvedand simplified direction finder circuits employing sat urable core inductors? These and other anddncidental' objects will becoineapparent to those sk illed in the art -upon considerationof the-following description; with reference to the accompanyihgfdi'awing; of-which l i'gt 1" a schematicc-i-rcuit diagram of-'a prereared emlcodiment-ot invention, Fig? 2 is a,

vector diagram illustrating the: operatiomoi=- the circuit of Fig. 1, and Fig. 3 is a circuit, diagram of a modification of Fig. 1.

Referring toFig. 1,a loop antenna l is conI-' nected' in series "with an inductor 3to thegridcathode circuitof an amplifier tubezS: The-loop and inductor aretuned by: a variable condenser T. The-inductor 3 is provided with a ferromagnetic core 9, such as a body of c'omm'inuted magfnetite with. a binderof insulating" materiak A non-directive antenna I I. is connected to the plate circuit of? the'tube- 5; which includes: the resonant circuit-I31 l5: This'ci'r'cuit-is coupled to the inputof' a radio receiver I! thr'ough a capacitonlfi. The output of thereceiver IT is connected to the' movable coi1'2'l of arleft-ri'ght indicator 232. A low frequency oscillator 25 is connected to "the stator coil 2'! of the indicator 23 through a -blockingi condenser 26 and to a winding -surrounding the-core 9 throughla D'.-C.- source such as-a-= battery 28;

'I-heoperation oi the system is as follows The tuning condensers l and I3, and the radio re ceiver i are adjusted'sethat the antenna and receiver-circuits resonate at the desire'd f'req'uen'cyf The controls may be ganged for simultaneous" operation; as indicated by: the dashed line 3 1; The oscillator 25 operating at a frequency of; for example,-- 1000- cyclesper second; energizesthe winding 29 and periodically varies the inductance of the winding 3 by magnetic saturation of the core 9% The resonant frequency of the 1 circuit comprising the loop thecoridenserli and the inductance 3- is accOrdingIy Varied at -the osil lator 'frequenci The resultant signal outp'ut of this circuit passes through the amplifier i an'd is combined in the circuit l3} l5 with the signal from 'tlie antenn'a I The effect of' modulating" the tuning of" the loop circuit is illustrated: vectoriall'y'in Fig. 22 Thevector'A represents'th'e signal-from the nondirectional antenna II. The loop'voltageL istin quadrature phase'with' respect to the Voltage: h when-the loop circuit i's'tuned to resonance; The vectors L'" and "L' "represent*the loop circuitvolt age as the tuning is varied slightly above and below resonance; shifting theph'ase of 'the voltage in oppositedirectionsj Theresultants R, R' and R" are produced by the -addition-of the-Voltages L, L' and L" respectively to'the vol-cage A-.- The combined: input to the -radio -receiver varies over the ra n'ge of F p'h'ase: and' amplitude between the vectora R and R ificludes both' a mp1i tuaamodulaticn a-nd phase; or frequency 'modirlatiofi; and may be detected the 3 receiver IT 3 by a frequency discriminator circuit or by a rectifier.

In either event, the output of the receiver I1 is a voltage varying at the frequency of the oscillator 25 between two values corresponding to the lengths of the vectors R' and R" of Fig. 2, or if a frequency responsive detector is used, to the angles of thetwo vectors with respect to some reference line, determined bythe discriminator adjustment. When the angle of the loop with respect to an arriving wave is such as to pick up no signal, vectors R and R" are both equal to and identical with A, and the operation of the V oscillator 25 causes no variation in the receiver output, as the loop is turned in one direction from the null position the vector L becomes longer, causing the vector R" to become progressively longer than the vector R. in the other direction from the null, the vector L increases in a reverse-direction as indicated by the dotted lines, and the vector R becomes greater than R", I

The receiver output energizes the moving coil 2| of the device 23. The stationary coil 21 is energized by the alternating current output of the oscillator 25, and consequently causes the response of the indicator 23 to the receiver output to be periodically reversed in synchronism'with the loop modulation.

Thus the coil 2| tends to deflect first one way and then the other. If the voltages R" and R" are equal the alternate torques balance each other and no deflection occurs. If one exceeds the other, the indicator is deflected to the left or right according to the direction of wave arrival with respect to the axis of the loop.

Fig. 3 shows a modified form of the invention,

comprising a loop I, a vertical antenna II, and loop modulating transformers 33 and 35 arranged to be operated by a low frequency oscillator 25. The receiver, indicator, and other parts of the system maybe, identical with the corresponding parts of the system of Fig. 1. The loop I is, connected to the primaries of the transformers 33 and 35in opposite, polarities. The transformer secondaries are connected in the same polarity to the amplifier 5. saturating windings 31 and 39 are provided on the cores of the transformers 33 and 35 and connected through adirect current source, such as a battery M, to the oscillator 25.

.In operation, the cores of the transformers 33 and 35are saturated alternately, so that more energy from the loop is transferred through one and then the other. This results, in eifect, in periodic reversal of the loop voltage at the amplifier input. The sum of thetransformer inductances coupled into theloop circuit remains substantially constant, so the tuning is not varied by the oscillator 25 and the loop output is amplitude modulated as in the usual balanced modulator arrangement.

, Thus the invention has been described as an improved automatically indicating direction finder, employing magnetically saturable inductance means for left-right antenna switching. Considerable simplification of the required circuits and apparatus is achieved, with corresponding reduction of space and weight requirements.

I claim as my invention:

1., A radio direction finder comprising a directive antenna, a non-directive antenna, a generator of low frequency oscillations, reactance means in the circuit of, one of said antennas, means for varying said reactance in response to said low As the loop isturned frequency oscillations, means for combining the outputs of said antennas, a demodulating circuit connected to respond to the combined antenna output, and an indicator responsive to the combined outputs of said demodulating circuit and said low frequency generator.

2. The method of indicating the azimuth of arrival of a radio wave at :"an antenna system comprising the steps of deriving fro'm said wave a signal related in amplitude to the said azimuth,

deriving from said Wave a second signal independent in amplitude of said azimuth, cyclically shifting the phase of one of said signals through an angle substantially less than combining the phase-shiftedsignal with the other of said signals, demodulating the combined signal, and comparing the amplitudes of alternate maxima of the demodulated signal.

3. A radio direction finder comprising a directive antenna, a non-directive antenna, a generator of .low frequency oscillations, an inductor connected in the circuit of one of said antennas, said inductor being provided .with a saturable ferromagnetic core, a winding for varying the magnetization of said core connected to said low frequency oscillator, a, circuit for combining the outputs of said antennas, a detector connected to respond to the combinedantenna output, and an indicator connected to said detector and to said oscillator so as to respond in opposite senses to said detector output during successive half cycles of said oscillator.

4. A radio direction finder comprising a directive antenna, a non-directive antenna, a generator of low frequency oscillations, transformers provided with saturable cores and with their primaries connected in unlike sense to the circuit of one of said antennas and their secondaries connected in like sense to a common impedance, means for combining the resultant of said transformer outputs with the output of the other of said a'ntennas, means connected to said oscillator for alternately saturating the cores of said transformers, and an indicator arranged to respond to the combined antenna outputs in one sense while one of said cores i saturated and in the opposite sense while the other of said cores is saturated. V I v I 5. A radio direction finder comprising a directive antenna, a non-directive antenna, a generator of low frequency oscillations, inductance means provided with a saturable ferromagnetic core and connected in the circuit of one of said antennas, a winding connected tov said low frequency generator for varying the magnetization of said core whereby the reactance included in said antenna circuit is varied in response to said low frequency oscillator, means for combining the outputsofsaid antenna, a demodulating circuit connected to respond to the combined antenna output and an indicator responsive to the combined outputs of said; demodulating circuit and said low frequency generator.

WENDELL L. CARLSON.

nuFERENcEs CITED The following referenceszare of record in the file of this patent;

UNITED STATES ATENTS Number I Name H Date- 2,254,943 Galle Sept. 2, 1941 2,286,804 Hooven June 16, 1942 2,279,151 Wal1ace; Apr. '7, 1942 2,159,754 Woh1farth May 23, 939 

